This application is based on and claims priority under 35 U.S.C. xc2xa7119 with respect to Japanese Application No. 2000-094620 filed on Mar. 30, 2000, the entire content of which is incorporated herein by reference.
This invention generally relates to an exhaust gas recirculation (EGR) system in an automobile engine and the like. More particularly, the present invention pertains to an EGR system for purifying harmful products contained In the exhaust gas of an engine and efficiently absorbing heat energy contained in the exhaust gas to assist engine warm-up using the heat energy.
Over the years, much development work has been performed with respect to engines functioning as a power source for an automobile. Environmental concerns have contributed to the recognition that purifying the engine exhaust gas and improving the efficiency of the engine performance are important.
A publication entitled xe2x80x9cMotor Fan additional volume, All about New Model Pajeroxe2x80x9d (Pages 23 and 24, Oct. 23, 1999, Sanei-shobo Publishing Co., Ltd.) discloses a known system to purify harmful products contained in the exhaust gas. With this system, exhaust gas emitted from an engine unit is recirculated back to the intake side via an EGR passage. Additionally, the recirculated exhaust gas quantity is regulated in accordance with the degree of opening of an EGR valve, so that the EGR system is able to purify the harmful products contained in the exhaust gas.
The EGR passage is provided with a water-cooled heat exchanger, oftentimes called an EGR cooler. The EGR cooler is able to refrigerate or cool the exhaust gas recirculated thereto from 300 degrees centigrade down to 180 degrees centigrade. By lowering the temperature of the exhaust gas recirculated to the intake side, the recirculated exhaust gas quantity can be increased. Therefore, this known EGR system possesses improved charging efficiency to fill the engine unit with fresh air, thereby reducing the production of NOx (nitrogen oxide) and minimizing emission of PM (particulate matters) including black smoke.
As mentioned above, the improvement in the efficiency of the engine performance produces an environmentally-friendly effect, including improved fuel economy.
However, improvements in the efficiency of the engine performance may cause drawbacks. For example, the engine may require a long time to warm-up, and the heating performance of the engine may degrade. These drawbacks may affect the driving comfort and stability of the automobile.
A need thus exists for a system that is able to improve purification of the exhaust gas, while at the same time improving engine warm-up and the efficiency of the engine performance.
It would be desirable to provide a system that assists the engine warm-up using heat energy contained in the exhaust gas.
It would also be desirable to purify harmful products contained in the exhaust gas.
According to the present invention, an exhaust gas recirculation (EGR) system in an engine system includes an intake passage, an exhaust passage, and an EGR passage diverging at a first diverging portion in the exhaust passage. The exhaust gas flowing through the exhaust passage is recirculated via the EGR passage into the intake passage. The EGR passage is further provided with a heat exchanger and an EGR valve. A second diverging portion is defined in the EGR passage downstream from the heat exchanger and a merging portion is defined in the exhaust passage downstream from the first diverging portion. A connecting passage fluidly connects the second diverging portion and the merging portion. An exhaust gas regulating valve is mounted at the first diverging portion or at the merging portion in the exhaust passage, wherein the exhaust gas quantity recirculated into the connecting passage is adjustably regulated by the exhaust gas regulating valve.
When the exhaust gas regulating valve mounted at the first diverging portion or at the merging portion is set to a fully closed position (fully cutting off airflow from the exhaust passage into a muffler via a catalyst), the exhaust gas is recirculated back to the exhaust passage via the first diverging portion, the heat exchanger of the EGR passage, the connecting passage, and the merging portion. When the exhaust gas regulating valve is set to a fully opened position (fully fluidly connecting the airflow from the exhaust passage to the muffler), the fluidly connected airflow from the exhaust passage to the connecting passage is interrupted, therefore the aforementioned EGR through the connecting passage does not occur. However, based on the opening degree of the EGR valve, the exhaust gas can be recirculated back into the intake passage via the first diverging portion and the heat exchanger of the EGR passage. Additionally, the exhaust gas regulating valve can be set to an intermediate position between the opened and closed positions as well.
The high temperature exhaust gas flowing through the exhaust passage is fluidly diverged or diverted into the EGR passage, whereby the exhaust gas heat energy warms up the engine coolant by heat exchange at the heat exchanger. This mechanism can effectively raise the coolant temperature and improve the engine warm-up.
In more detail, the recirculated exhaust gas quantity is regulated in correspondence with the temperature of the engine coolant. When the engine coolant temperature is less than a predetermined value, the exhaust gas regulating valve is set to the fully closed position, wherein the exhaust gas quantity flowing into the connecting passage is at a maximum. When the engine coolant temperature is equal to or larger than the predetermined value, the exhaust gas regulating valve is set to the fully opened position, wherein the exhaust gas quantity flowing into the connecting passage is at a minimum.
When the coolant temperature is less than the predetermined value and sufficient engine warm-up is not achieved, the high temperature exhaust gas flowing through the exhaust passage is fluidly diverged or diverted into the EGR passage, whereby the exhaust gas heat energy can warm up the engine coolant by way of heat exchange at the heat exchanger. The coolant temperature can thus be effectively raised to improve the engine warm-up.
Additionally, the recirculated exhaust gas quantity is regulated in correspondence to the engine speed and the engine load. When the engine speed is low and the engine load is small, the exhaust gas regulating valve is set to the fully closed position, wherein the exhaust gas quantity flowing into the connecting passage is at a maximum. Corresponding to an increase of the engine speed and the engine load, the exhaust gas regulating valve is orderly set to the intermediate position and at the fully opening position, wherein the exhaust gas quantity flowing into the connecting passage is decreased.
Even when sufficient engine warm-up is not achieved, the EGR system of the present invention can decrease the exhaust gas quantity recirculated into the connecting passage and increase the exhaust gas quantity directed through the exhaust passage to the muffler based on the increase of the engine speed and the engine load. The EGR system of the present invention thus does not degrade the exhausting performance.
Furthermore, the recirculated exhaust gas quantity is regulated in correspondence to the catalyst temperature. When the catalyst temperature is low, the exhaust gas regulating valve is set to the fully opened position, wherein the exhaust gas flows into the connecting passage at a minimum. With an increase in the catalyst temperature, the exhaust gas regulating valve is orderly set to the intermediate position and the fully closed position, wherein the exhaust gas quantity flowing into the connecting passage is increased.
Even when sufficient engine warm-up is not achieved, the EGR system of the present invention can decrease the exhaust gas quantity recirculated into the connecting passage corresponding to the low catalyst temperature. Therefore, this mechanism can effectively increase the exhaust gas quantity directed from the exhaust passage to the catalyst and the muffler, wherein the catalyst warm-up is efficiently improved.
Additionally, another exhaust gas regulating valve can be mounted in the EGR passage between the heat exchanger and the EGR valve. The other exhaust gas regulating valve is closed when the exhaust gas regulating valve is positioned at the fully closing position or at the intermediate position. Therefore, high temperature exhaust gas does not flow into the EGR valve. Thus, the other exhaust gas regulating valve effectively prevents the high temperature exhaust gas from flowing to the EGR valve, whereby thermal damage to the EGR valve is minimized.
Thus, considering the exhaust gas emitted through the engine unit and recirculated into the intake side via the engine coolant corresponding to the engine speed, engine load, catalyst temperature, the EGR system can improve the engine warm-up and at the same time purify the exhaust gas to retain the exhausting performance.
In accordance with another aspect of the invention, an engine exhaust gas recirculation system includes an exhaust passage extending from an exhaust manifold of an engine, a muffler disposed along the exhaust passage, an EGR passage communicating with the exhaust passage at a point upstream of the muffler to direct the exhaust gas from the exhaust passage towards a heat exchanger mounted in the EGR passage, a connecting passage fluidly connected to the EGR passage at a point downstream from the heat exchanger and fluidly connected to the exhaust passage at a point downstream from where the EGR passage communicates with the exhaust passage, and an exhaust gas regulating valve mounted between the muffler and the point at which the EGR passage communicates with the exhaust passage.